Malocclusions between the upper and lower jaws of a patient generally fall within three classes. Class I malocclusions are those in which the individual teeth are not aligning well with each other and with the corresponding teeth in the opposite jaw. This malocclusion is commonly corrected with braces applied to the teeth for gradual realignment. Class II malocclusions relate to those cases in which the lower jaw is not developing in the manner which allows the upper and lower arches of teeth to come together with a proper bite or alignment to one another. More specifically, in this type of malocclusion an overbite condition exists and must be corrected by moving the lower jaw forward to obtain a proper bite. Corrective appliances are therefore used to hold the lower jaw in a proper bite position so that the jaw bones and muscles will support the proper bite. Class III malocclusions occur when the lower jaw is positioned too far forward with respect to the upper jaw. This condition, often referred to as an underbite, is typically corrected with the use of braces and rubber bands and, in some cases, through surgery.
The present invention generally relates to appliances for treating Class II or Class III malocclusions or, respectively, overbite and underbite conditions. In the past, rubber bands and springs extending in tension between upper and lower sets of brackets have been used to move the jaws into alignment as the patient closes their mouth. Over time, this corrective movement will permanently realign the upper and lower teeth of the patient through muscle development and/or proper bone growth. External head gear attached to the braces of the patient has been used for similar purposes. One main disadvantage with these treatment options is that they each require cooperation on the part of the patient. In other words, the patient is required to regularly maintain the rubber bands or head gear in place. Patients may choose not to apply the corrective appliances because they are unsightly or uncomfortable or may forget to apply them. In either case, the lack of diligence in using the corrective appliances reduces the effectiveness of the treatment.
Various bite fixing appliances have also been developed to overcome the disadvantages of rubber bands, springs, head gear or other methods of treating Class II and Class III malocclusions. Several of these appliances involve the use of coil springs connected between upper and lower sets of braces in a patient's mouth. Examples may be found in U.S. Pat. Nos. 3,618,214; 4,708,646; 5,352,116; and 5,846,074. These and other similar bite correcting appliances each suffer from various disadvantages. For example, the appliance described in U.S. Pat. No. 3,618,214 uses superimposed springs to pull a patient's lower jaw forward. This design is prone to mechanical failure and is undesirable for at least this reason. Also, this device is designed to apply a constant pulling force when the patient's mouth is in a closed position and this pulling force increases as the patient opens their mouth. This can be uncomfortable for many patients.
The device disclosed in U.S. Pat. No. 4,708,646 attempted to alleviate some of these concerns, however, the coil spring of this patent is an open coil spring secured within a resilient plastic so as to be nonstretchable. This design is prone to increased incidents of breakage or, in other words, subject to a short fatigue life. The open coil spring and the nonstretchable properties of the appliance increase the amount of stress on the spring and cause the stress to be applied over a shorter length of spring wire. Thus, the spring breaks with undesirable frequency.
U.S. Pat. No. 5,352,116 similarly relates to the use of a sheathed coil spring connected between upper and lower teeth of a patient to provide a pushing force to the lower jaw. As with the appliance shown in U.S. Pat. No. 4,708,646, this appliance can be difficult to install and reinstall. Also, although this appliance uses a stretchable spring, the spring is an undesirable open coil spring design.
U.S. Pat. No. 5,846,074 discloses the use of a coil wire sheath, however, the sheath is configured as an open coil compression spring. This spring presses against opposite connecting pieces as an internal straight wire spring element contained within the sheath is flexed when the mouth moves to a closed position. As stated in the patent, the coil spring does not supply significant pushing force and is not connected to the attachment structure at each end. The function of the coil sheath is to promote comfort and capture any broken pieces of the internal straight wire spring.
In general, the prior bite fixing appliances have provided inadequate treatment options for many patients and even the best appliances are in need of improvement in such areas as increasing fatigue life, easing installation and removal, and simplifying the overall construction.